1. Field of the Invention
The present invention relates to a golf club head. More specifically, the present invention relates to a golf club head with a face insert.
2. Description of the Related Art
High performance drivers employ relatively thin, high strength face materials. These faces are either formed into the curved face shape then welded into a driver body component around the face perimeter, or forged into a cup shape and connected to a body by either welding or adhesive bonding at a distance offset from the face of up to 0.75 inch. In a popular embodiment of the sheet-formed face insert driver, the weld between the formed face insert and the investment cast driver body is located on the striking face, a small distance from the face perimeter. It is common practice for the face insert to be of uniform thickness and to design the surrounding driver body component to be of equal thickness. In this way there is continuity of face thickness across the weld.
Most face inserts are composed of a titanium alloy material. Titanium alloys are generally classified into three types depending on the microstructure of the material developed after processing of the material. The three types are alpha alloys, alpha-beta alloys and metastable alloys, and these represent the phases present in the alloy at ambient temperatures. At ambient temperatures, the thermodynamic properties of titanium favors the alpha phase. However, alloying titanium with other elements allows for the high temperature beta phase to be present at ambient temperatures, which creates the alpha-beta and metastable beta microstructures. The metastable phase may be transformed into the alpha phase by heating the alloy to an intermediate elevated temperature, which results in a metastable titanium alloy with increased static strength.
Such high strength metastable titanium alloys have been used as face inserts for drivers with a high coefficient of restitution. However, the heat treatment process compromises the toughness of the material, where toughness is defined as the resistance of the material to fracture under loading. Thus, even heat treated, high strength, metastable titanium alloys have limited application as face inserts due to inferior fracture properties. Thus, there is a need for face inserts composed of titanium alloys with an appropriate microstructure for better fracture properties. This requires a proper balance between strength and toughness (resistance to fracture), without a substantial increae in the costs associated with manufacturing the face insert.
Several patents discloses face inserts. Anderson, U.S. Pat. Nos. 5,024,437, 5,094,383, 5,255,918, 5,261,663 and 5,261,664, disclose a golf club head having a full body composed of a cast metal material and a face insert composed of a hot forged metal material.
Viste, U.S. Pat. No. 5,282,624, discloses a golf club head with a cast metal body and a forged steel face insert with grooves on the exterior surface and the interior surface of the face insert and having a thickness of 3 mm.
Rogers, U.S. Pat. No. 3,970,236, discloses an iron club head with a formed metal face plate insert fusion bonded to a cast iron body.
Galloway, et al., U.S. Pat. No. 6,354,962, discloses a golf club head of a face cup design.
Some alloy materials that have desired inherent properties such as yield strength, tensile strength and hardness often have high densities, which limit the utilization of such materials in golf club heads. However, there is a need for a golf club head with a face insert that has the inherent properties of these materials while allowing for more discretionary mass than conventional face insert golf club heads.